Množina: diapasons

ETYM Latin, from Greek diapason (i.e., diapason chordon symphonia the concord of the first and last notes, the octave); dia through + paswn, gen. pl. of pas all: cf. French diapason. Related to Panacea.
Loud, harmonious burst of music; entire gamut or compass; principal organ-stop.
Either of the two main stops on a pipe organ; SYN. diapason stop.
In music, the principal stop of an organ, which gives the instrument its characteristic tone quality. Diapasons may be “open”, producing a bright color, or “stopped”, producing a muffled but sweet tone. The equivalent stop on a German-built instrument is the Prinzipal. In French usage, “diapason normal” is the equivalent of concert pitch.